1. Field of the Invention
The present invention relates to a lens-shutter coupling unit to be used for an optical instrument, such as an camera, and having a coupling structure of a mechanical shutter and a lens shutter.
2. Description of the Related Art
In the related art, a camera or the like including an image pickup optical system composed of a plurality of lenses has been used widely. An object image that is formed on the basis of a light beam entering the image pickup optical system is focused on an image pickup device, such as an image sensor using a charge-coupled device (CCD), i.e., a CCD image sensor, which is disposed in a predetermined position. In such a camera, in order to facilitate incorporation of the camera into a portable terminal in addition to enhancements in functions, such as a zooming function and a focusing function, and realization of high resolution, the camera is desired to be further reduced in size. Therefore, it is indispensable to miniaturize a light-quantity adjuster, such as a shutter unit for adjusting the quantity of light according to the brightness of an object. Generally, the size of the shutter unit depends on the diameter of an exposure opening, an arrangement space for shutter blades that shields the exposure opening, an ND (Neutral Density) filter, and the like, and an arrangement space for driving units for operating the shutter blades, the ND filter, and the like. Further, generally, a camera having a zooming function is configured such that a zooming lens group and a shutter unit are operated integrally in order to decrease the diameter of the opening.
In an example of the configuration for miniaturizing the shutter unit, a step motor is disposed around a lens barrel (lens holder) to operate shutter blades (for example, see Japanese Unexamined Patent Publication JP-A 62-131238 (1987) (FIGS. 1 and 2)). Further, the configuration of a lens holding frame (lens holder) for attaching a lens to a shutter unit is also disclosed (for example, see Japanese Unexamined Patent Publication JP-A2002-318335 (FIGS. 1 and 2)). The lens holding frame includes a lens receiving barrel and an arm part. The lens receiving barrel receives the lens so as to surround a periphery thereof, and the barrel is provided with a lens supporting part that abuts on the other surface of the lens. The arm part is formed integrally with the outer periphery of the lens receiving barrel, and is bent in the direction of an optical axis when it is connected to a connecting part provided in the shutter unit to push the lens barrel unit against the shutter unit. A biasing force generated by bending of the arm part causes the lens to be sandwiched between the lens supporting part and a lens abutting surface of the lens shutter, thereby facilitating positional adjustment and holding of the lens.
In the configuration disclosed in JP-A 62-131238, a driving unit for the shutter blades is disposed at an outer periphery of the lens holder. The lens holder has such a thickness that it receives the lens. Accordingly, the driving unit has to be disposed further outside than the outer diameter of the lens by the thickness of the lens holder, and consequently the shutter unit cannot be reduced in size sufficiently. Further, since the driving unit is disposed in a position apart from the optical axis, and the center of rotation of the shutter blades is apart from the optical axis, it is necessary to enlarge the shutter blades themselves, and therefore it is difficult to miniaturize the shutter unit.
In the configuration disclosed in JP-A 2002-318335, in order to align the lens with the shutter unit, it is necessary to adjust the position of the lens, and consequently the assembling becomes complicated. Further, the publication does not disclose a configuration to miniaturize the shutter unit.